1. Field of the Invention
The present invention relates generally to the manufacture of continuous seam-welded metal tubes or pipes, and more particularly to a system for observing the axial alignment of the pipe or tube as it is fabricated and continuously correcting the alignment in response to observed deviations so as to produce tubes having a high degree of axial alignment or straightness.
2. Description of the Prior Art
In accordance with a well-known procedure for fabricating seam-welded pipes and tubes, a continuous strip or skelp is advanced through a forming apparatus and progressively deformed into a tubular form having an open, longitudinally extending seam. The tubular form then advances through a welding station wherein the adjacent longitudinal free edges are urged together and joined by a suitable welding process. The particular process to be employed will generally be dictated by, among other factors, the material from which the tube or pipe is formed. For example, the pipe may be formed of low carbon steel, stainless steel, aluminum, etc., and the welding process may include any of the well-known welding techniques conventionally employed with the various materials. In a widely used embodiment the tube or pipe is heated by electrical induction so that the edges achieve fusion temperature, and the heated edges are urged into engagement to produce a continuous monolithic welded seam.
Following the welding step, the pipe or tube may advance through a scarfing unit for removal of the raised bead created incident to the formation of the welded seam, and then through a series of sizing rolls for imparting the precise diameter and cross-sectional configuration to the formed pipe. Finally, after the continuous pipe has been sized and cooled, it enters a cut-off mechanism wherein it is cut into sections of appropriate length.
Due, among other factors, to residual stresses in the material following formation of the pipe, and the heating and cooling incident to the welding of the seam, the pipe may tend to warp or snake and develop an undesirable non-linear configuration as it exits the constraints of the forming and welding mechanism. In order to minimize the amount of this curvature in the finished product, the pipe or tubing is directed through a straightening unit wherein appropriate forces are applied by straightening rolls to bend the pipe to compensate for existing curvature and cause it to assume a linear profile as it exits the forming apparatus. Heretofore, the pipe has been observed at some distance downstream from the straightening unit by an operator to visually determine the amount and orientation of existing curvature, and the straightening unit then manually adjusted in response to the observed condition to compensate for the curvature. The procedure functions well for its intended purpose, and permits production of pipe of good quality. However, it has not been found entirely satisfactory in that it is dependent upon the operator's visual observation and subsequent manual adjustment of the straightening unit. It is thus subject to the operator's judgment, as well as human error. In addition, deviation of the pipe is best observed at some distance downstream from the straightening unit, typically in the cut-off area. Since the pipe advances at a relatively rapid rate, a significant amount of defective pipe may be produced between the time at which deviation is noted and corrective action can be taken at the straightening unit.